A member composed of glasses laminated together is superior in soundproof property, adiathermancy, heat resistance, airtightness and the like, and therefore it has been used as an architectural window glass, and a display glass of TV or the like. In addition, a member composed of a glass and a metal plate which are glued together, or a member composed of a glass and a ceramic material which are glued together has been often used as a substrate for packages including IC chips.
Conventionally, a solder with lead, a lead glass frit, and various filter mediums, brazing sheets, and polymer organic adhesives described in “JIS handbook(3) HITETSU (non-ferrous metal)” have been used as an adhesive in bonding members as described above. However, it is not preferable to use a glass frit and a solder, both containing lead because of environmental concerns, and use of them will be banned in the future.
Japanese Unexamined Patent Publication (JP-A) No. 2001-139345 has suggested, as a lead-free glass frit, a glass composition which comprises: 2 to 20 mol % of SiO2; 15 to 35 mol % of Bi2O3; 2 to 15 mol % of a component (LiO2, Na2O, or K2O) for lowering a softening point and raising the fluidity; and 20 to 50 mol % of devitrification restraining component (ZnO). JP-A No. 2003-183050 has suggested a lead-free frit made from a SnO-P2O5-based glass powder.
However, the Bi2O3-based glass frit disclosed in JP-A No. 2001-139345, and the SnO-P2O5-based glass frit disclosed in JP-A No. 2003-183050, involve the problems that the glass may be broken, a crack may be produced in a bonding material, and a phenomenon of unsticking may be caused, in the case of bonding between substrates different from each other in linear thermal expansion coefficient, such as between glasses different from each other in linear thermal expansion coefficient, and between a glass and a ceramic material.
On the other hand, where a polymer organic adhesive agent is used at a high temperature of 250° C. or higher, an organic component thereof is carbonized to weaken the adhesion strength, and thus the airtightness cannot be held.
Therefore, where a conventional lead-free bonding material is used as a bonding material for bonding together base materials or substrates which are different from each other in linear thermal expansion coefficient, it is difficult to achieve the desired heat resistance, airtightness and bonding strength.